Conventionally, an insulating tape or sheet has been used for covering a conductor in an electric wire for insulating and protecting same. It comprises an adhesive layer formed on a polyester film, which is a substrate for the tape or sheet. Various adhesives such as polyolefins, thermosetting resins and polyester adhesives have been used for the aforementioned adhesive layer.
Of the aforementioned adhesives, polyolefin adhesives are advantageous in that they do not cure at room temperature, permitting easy handling thereof, and are most inexpensive in cost.
When an insulating tape or sheet having a polyolefin adhesive layer is used as an insulating material for an insulated wire to be used under severe conditions in the electric system of, for example, an automobile, however, the wire is susceptible to trouble due to the deformation and breakage of the wire, which is caused by a physical impact. When the wire is used in a bent state for a long time, moreover, the insulated wire experiences insulation failure due to the partial separation of the insulating layer from the adhesive layer in the insulating tape or sheet, or between the tape or sheet and the conductor, or due to the occurrence of cracks in the tape or sheet, posing problems to be solved.